Since the earliest times of electrical sound reproduction there has been a continued trend toward ever more realistic and distortion free sound reproduction and methods. Almost all microphones now in use employ some form of a physical diaphragm which is exposed to the sound waves and which in turn is coupled to some form of electrical receiver which translates the vibrations of the diaphragm into electrical signals which can be amplified in suitable amplifiers and connected to loudspeakers or sound recording equipment.
In the oldest form of microphone a diaphragm is connected to a small chamber filled with carbon granules which is traversed by an electrical current which is modulated by the variable resistance of the carbon granules. In more modern microphones the diaphragm is coupled capacitively through a small air space to one electrode of a small capacitor such that the capacitance is modulated by the vibrations of the diaphragm. In another class of microphones, the diaphragm is coupled to an inductor placed in a magnetic field such that the vibration of the diaphragm is translated into a low level alternating potential in the conductor.
It follows that whenever a physical diaphragm with even a small but finite mass is interposed between the sound waves and the electrical receiving apparatus, the physical properties of the diaphragm, such as mechanical resonances and standing waves have a distorting effect on the translation of sound waves into electrical signals.
Another source of loss of fidelity in electrical sound reproduction and recording systems stems from the fact that existing microphones have only one sound channel which may receive sound primarily from one direction or from many or all directions depending on the construction of the microphones, but a human being with binaural hearing and situated in an auditorium or listening room listening to a stage performance will hear sounds coming from all directions as sound waves are reflected from all surfaces of the room. For that reason the microphone according to the instant invention, in a preferred embodiment has a plurality of sound channels, which, when connected to a similar plurality of loudspeakers that are oriented in a configuration corresponding to the orientation of the individual sound channels of the microphone, may serve to produce sound reproduction that may have a degree of fidelity approaching that of a lifelike listening situation.
It is an important object of the instant invention to produce a microphone that uses laser beams such that the sound waves are sensed by means of phenomena relating to the interaction between sound pressure waves and a beam of laser light without an interposed physical diaphragm or, as in one embodiment, by a diaphragm or, as in one embodiment, by a diaphragm that may be of very small size and low mass which is not encumbered by mechanical resonances and standing waves encountered by the use of a diaphragm of the size normally used in microphones.
It is another important object of the present invention to produce a microphone utilizing phenomena related to the interaction between a beam of coherent laser light and acoustic sound waves to generate an electrical alternating signal which represents closely the alternating pressure of the sound waves, and such that a high degree of fidelity in the correlation between the sound wave and the resulting electrical signal is attained.
It is a further important object of the present invention to produce a microphone utilizing phenomena related to the interaction between a beam of coherent laser light and acoustic sound waves to generate a plurality of electrical signals, each signal representing closely the alternating pressure of a similar plurality of sound waves incident to the circumference of the microphone from a similar plurality of directions and such that all directions are separated by equal angles from each other in a generally horizontal plane.
It is another important object of the present invention to produce a microphone which is relatively easy to fabricate in large numbers without undue complexity and difficulty in the manufacture thereof.